1. Field of the Invention
This invention relates to a variable magnification reproduction machine and, more particularly to an optical scanning system which provides the capability of attaining continuous changes in scanning rates to provide a range of magnification.
2. Prior Art
In variable magnification reproduction machines having scanning optical systems, the selection of a desired magnification value is generally associated with a corresponding selection of optical scanning speed and distance of travel. In such machines, to obtain smaller magnification ratios, a document is scanned at a faster rate and the distance of travel is simultaneously extended so that a larger document may be reproduced using the available photoreceptive surface. Prior art machines which provide for scanning systems adapted for operation with discrete values of magnification changes are disclosed in representative U.S. Pat. Nos. 3,542,467, 3,614,574, 3,778,147, 3,884,574, 3,897,148, 4,142,793 and 4,027,963. Scanning systems which can accommodate a greater range of reduction values are disclosed in U.S. Pat. Nos. 4,124,293 and 4,093,374, both of which uses a plurality of cams connected to the drive system. Each cam provides a drive speed specific to a given reduction.
It is desirable to provide a greater range of continuous speed changes to a scanning optics system for magnification control without recourse to increasing the number of drive cams. Such systems have been provided as shown in U.S. Pat. Nos. 4,120,578 and 4,095,880. Both patents disclose a drive cam shaped so as to provide a constant velocity to the optics drive carriage of the particular system. In each patent, cam follower means are adapted to provide continuous variations in scan velocity depending on the reduction mode initiated.
In the '880 patent this scan rate change is accomplished by changing the orientation of a cam follower arm by moving a yoke along a rail. In the '578 patent, a drive carriage was mounted in a track which was PG,3 positioned in a continuously variable manner along a lead screw. These systems provide the desired solutions but at a price of increased cost and complexity.
It is therefore desirable to provide a scanning optics system which will provide continuous variable scanning speeds consistent with a wide range of reduction values and which will accomplish this purpose in an efficient, relatively inexpensive and simple manner.